1. Field of the Invention
The present invention generally relates to a light source module. More particularly, the present invention relates to a laser module.
2. Description of Related Art
Referring to FIG. 1, a conventional Novalux extended cavity surface emitting laser (NECSEL) 100 includes a light emitter 110, a volume Bragg grating (VBG) 120 and a periodically poled lithium niobate crystal (PPLN crystal) 130. The light emitter 110 includes a light emitting layer 112, a p-type distributed Bragg reflector (DBR) 114 and an n-type DBR 16. The p-type DBR 14 and the n-type DBR 16 are disposed on two opposite sides of the light emitting layer 112, respectively. The light emitting layer 112 is capable of emitting an initial infrared (IR) beam 112i. The initial IR beam 112i passes through the n-type DBR 116, passes through the PPLN crystal 130, is reflected by the VBG 120, returns to the PPLN crystal 130, passes through the PPLN crystal 130, passes through the n-type DBR 116, passes through the light emitting layer 112, and is reflected by the p-type DBR 14 in sequence. The p-type DBR 14 and the VBG 120 form an internal cavity C therebetween. After the initial IR beam 112i is reflected within the internal cavity C many times, the light emitting layer 112 generates stimulated emission and emits an IR beam 112a with coherence, and the IR beam 112a resonates within the internal cavity C. When passing through the PPLN crystal 130, a part of the IR beam 112a is converted 130 into a visible beam 112b by the PPLN crystal 130. The visible beam 112b with coherence is then pass through the VBG 120 and travels outward.
In the NECSEL 100, the transmission and reflection spectra of the VBG 120 are varied with the temperature of the VGB 120, and the wavelength corresponding to the maximum of beam conversion ratios of the PPLN crystal 130 is varied with the temperature of the PPLN crystal 130. Therefore, the temperature of the VBG 120 and the temperature of the PPLN crystal 130 preferably match each. Otherwise, the proportion of the beam conversion from the IR beam 112a to the visible beam 112b of the PPLN crystal 130 decreases because the wavelength of the IR beam 112a reflected by the VBG 120 deviates away from the wavelength corresponding to the maximum of beam conversion ratios of the PPLN crystal 130 at the temperature at that time. When the NECSEL 100 is in operation, the temperature of the VBG 120 is increased by absorbing a part of energy of the visible beam 112b, which causes the temperature mismatch between the VBG 120 and the PPLN crystal 130. In order to prevent the reduction of the proportion of the visible beam 112b converted from the IR beam 112a, the temperature of the PPLN crystal 130 is adjusted to make the temperatures of the VBG 120 and the PPLN crystal 130 match each other. In this way, the wavelength of the visible beam 112b, however, deviates away from a predetermined value. When the laser module 100 is applied in a projection apparatus, the wavelength deviation of the visible beam 112b makes the color temperature of the image projected by the projection apparatus deviate to an unfavorable value.